Catalysts have been used widely in the refining and chemical processing industries for many years. Hydroprocessing catalysts, including hydrotreating and hydrocracking catalysts, are now widely employed in facilities worldwide. These hydroprocessing catalysts typically produce increased yields, faster reaction times, and improved product properties when compared with prior (non-catalytic thermal) processes for converting crude oils into refined products.
Hydroprocessing catalysts typically employed in commercial application today are classified as “supported” catalysts. These catalyst supports, which are generally molecular sieves such as SAPO's or zeolites, are often composed of materials such as silica, alumina, zirconia, clay, or some hybrid of these. A more expensive material, which imparts much of the actual catalytic activity, is impregnated on the support. These catalytic materials typically include metals such as nickel, molybdenum, and cobalt. In some cases platinum, palladium, and tungsten may be used.
Recently, a new generation of hydroprocessing catalysts has emerged. These catalysts do not require a support material. The catalyst is instead comprised of unsupported, micron-sized catalyst particles, such as molybdenum sulfide or nickel sulfide. These catalysts, due to factors such as increased surface area and other factors not discussed here, are many times more active than traditional supported catalysts. Performance is greatly improved during conversion operations when compared to traditional supported catalysts. One area in which these highly active, unsupported catalysts are currently being employed is vacuum residuum hydrocracking. In the process of being utilized in residue hydrocracking service, these unsupported catalysts often suffer a high amount of metals (specifically vanadium) and coke deposition, which increases the need for fresh makeup catalyst.
One drawback to both supported and unsupported catalysts is their cost. Typically, replacement costs for an expensive noble metal catalyst may be a major operating expenditure item in a refinery or chemical plant. A market has thus emerged to reclaim spent catalysts, and specifically spent hydroprocessing catalysts, so that the valuable metals can be recycled. The current high price of various metals has driven this need even further. Several spent catalyst reclaimers are currently in business at various locations around the world. Unfortunately, however, these roasting (or pyrometallurgical) based reclaimers are designed to recover metals from supported catalysts.
Due to the high concentrations of valuable metals, specifically molybdenum and nickel, used in this new generation of unsupported catalysts, a need has been identified for an economical unsupported catalyst metals recovery process which depends upon a feedstock of spent catalyst free of oil for the greatest efficiency in catalyst recovery. Co-pending patent application, Ser. No. 11/192,522 discloses a novel process for the removal of metals from an unsupported spent catalyst. In this method the unsupported spent catalyst is subject to leaching reactions. Vanadium is removed as a precipitate, while a solution comprising molybdenum and nickel is subjected to further extraction steps for the removal of these metals. In this process it is important to provide an oil free recovered catalyst as a starting material for metals recovery and catalyst regeneration. The present invention addresses this need and provides a novel and economical method for removal of all hydrocarbon liquid materials from spent hydrocracking catalysts as a preliminary step to recovery of metals from the spent catalyst. Accordingly, the present invention is generally directed to a novel method for separating and recovering ultrafine particulate solid material from a suspension of the solid material and a hydrocarbon liquid comprising: (i) precipitation or flocculation of a heavy fraction of the hydrocarbon liquid such that the precipitated heavy fraction encapsulates the particulate solid material, (ii) separating the heavy fraction from the light fraction by centrifugation and, (iii) coking the precipitated combination to remove essentially all liquid hydrocarbon materials from the solid material to provide a dry solid material suitable for metals recovery and catalyst regeneration processes.
Various methods for separating fine catalyst solids from hydrocarbon liquids resulting from hydroconversion processes are known in the art. For example, U.S. Pat. No. 5,008,001 to Kitamura et al. discloses a method for separating catalyst solids from heavy oil that, in one embodiment, consists of centrifuging the oil and catalyst slurry and heat drying the resulting catalyst cake at temperatures and/or retention times limited so as to prevent or minimize coking of the remaining heavy oil. In another example, U.S. Pat. No. 6,511,937 to Bearden et al. discloses a method for recovering deasphalted oil and solvent deasphalted rock from a slurry hydroprocessing system and calcining the deasphalted rock at an extremely high temperature of about 1200° F. to produce an ash catalyst precursor which is recycled back to the slurry hydroprocessing system. In yet another example, U.S. Pat. No. 6,974,824 to Spena et al., discloses a system and method for recovering a catalyst from a slurry comprising the catalyst and residual hydrocarbons by heating the slurry to vaporize the hydrocarbons in a heater preferably designed to prevent coking. In a final example, U.S. Pat. No. 4,732,664 to Martini discloses a method for separating finely divided solid particles from a hydroprocessing liquid comprising precipitating asphaltenes from the hydroprocessing liquids whereby the precipitation process promotes the agglomeration of the solid particles and removing the agglomerated particles from the liquid by centrifugation. Drying of the solid product obtained from the centrifuge underflow is mentioned as a method for removal of the remaining hydrocarbon liquids.
It is an object of the present invention to improve upon the above disclosed methods of separating catalyst particles from a hydrocarbon liquid slurry thereof, which invention is further described below.